Surface Sensitive Raman Microscopy with Total Internal Reflection Illumination
Chris A. Michaels
A Raman microscope utilizing a total internal reflection (TIR), annular illumination geometry through a ZnSe solid immersion lens (SIL) is described. Spectra of a thin film sample of the transparent organic conductor poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) on a polyethylene terephthalate (PET) substrate are presented and compared to those from a conventional confocal Raman configuration. These spectra demonstrate a significant increase in surface selectivity upon the use of TIR illumination as the decay length of the evanescent excitation field limits the depth of sample probed in this configuration. Spectral interference from the underlying PET substrate layer is greatly reduced with TIR illumination. An increase in surface selectivity is also demonstrated for spectra acquired through the SIL with uniform illumination. Raman images of a micropatterned PEDOT:PSS film acquired with TIR illumination are also reported. Enhanced lateral resolution is realized in this configuration due to the immersion effect of the SIL, and the sampling depth is limited to 150 nm by the choice of illumination geometry. This results in analysis volumes on the order of tens of femtoliters, nearly two orders of magnitude smaller than typically achieved in conventional confocal Raman microscopes. This approach yields Raman spectra and images with surface selectivity significantly greater than can be achieved in confocal Raman, and provides a valuable tool for the microanalysis of thin surface films.
Surface Sensitive Raman Microscopy with Total Internal Reflection Illumination, Journal of Raman Spectroscopy, [online], https://doi.org/10.1002/jrs.2610
(Accessed December 8, 2023)